Then stop trying.
It'll happen naturally. Any fighting game I play, I main the character I feel most comfortable with naturally, and it's seldom if ever a conscious decision - I just come across a certain character and decide, "I like you. I'mma play you."
Try as I might, I can never seem to find another main in these games. I can play as other characters and have fun with them - hell, I may even be good with them - but I'll always end up coming back to that one character. That one character is my character and I love playing them. Smash is an exception, wherein I have two, but in general, I play one character primarily over the others. I can't even say how or why, I just do.
For example:
BlazBlue? Ooh, a cute kitty cat thing!
Tekken? Hey, that blonde-haired brawler is androgynous like me!
Street Fighter? Fighting schoolgirl, job done!
Skullgirls? This ninja nurse is pretty great!
Dead or Alive? I love that twin-tailed Gothic Lolita girl!
Smash? The two heroes from my all-time favourite game!
And so on and so forth.
The point is, you can't force these things, and you can't force yourself to enjoy the game or the characters. If you don't like any of the characters, then keep playing - you'll find one eventually, even, and perhaps especially, if you don't think you will.